The present exemplary embodiment relates generally to a fusing system for a printing system which includes one or more marking devices. It finds particular application in conjunction with a printing system which includes first and second marking devices and a secondary fusing module which enables desired final appearance or permanence characteristics to be achieved as well as maintaining uniform gloss characteristics between printed images generated by the marking devices, and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiment is also amenable to other like applications.
In a typical xerographic marking device, such as a copier or printer, a photoconductive insulating member is charged to a uniform potential and thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member, which corresponds to the image areas contained within the document. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with a developing material. Generally, the developing material comprises toner particles adhering triboelectrically to carrier granules.
The developed image is subsequently transferred to a print medium, such as a sheet of paper. The fusing of the toner onto paper is generally accomplished by applying heat to the toner with a heated roller and application of pressure. In multi-color printing, successive latent images corresponding to different colors are recorded on the photoconductive surface and developed with toner of a complementary color. The single color toner images are successively transferred to the copy paper to create a multi-layered toner image on the paper. The multi-layered toner image is permanently affixed to the copy paper in the fusing process.
Another approach employed to fuse toner to paper is to apply a high-intensity flash lamp to the toner and paper in a process known as “flash fusing.”
The fusing process serves two functions, namely to attach the image permanently to the sheet (fixing) and to achieve a desired level of gloss.
The reliability of color fusers tends to be low when compared with the other components of a printing machine and with black and white fusers. This is primarily because higher temperatures and longer nip dwell times are typically employed to achieve higher gloss levels for color images. To achieve a high gloss at reasonable temperatures, the surface smoothness (Ra) is generally about 0.4 microns or less. Over time, the color fuser roll tends to wear, resulting in non-uniformities in the surface of the roll, which, in turn, lead to gloss non-uniformities. Additionally, the lifetime of the fuser roll material is limited by the desire to provide compressibility to achieve an adequate nip width, which affects the dwell time for heating, and provide sufficient differential speeds to enable stripping and release.
Systems which incorporate several marking engines have been developed. These systems enable high overall outputs to be achieved by printing portions of the same document on multiple marking devices. Such systems are commonly referred to as “tandem engine” printers, “parallel” printers, or “cluster printing” (in which an electronic print job may be split up for distributed higher productivity printing by different printers, such as separate printing of the color and monochrome pages). In some systems, a process known as “tandem duplex printing” is employed. In this process, a first marking engine applies an image to a first side of a sheet and a second marking engine applies an image to a second side of the sheet. Each of the marking engines is thus operating in a simplex mode to generate a duplex print. This has been found to be more efficient for some applications than using a single marking engine with an internal duplex path to create a duplex print. In some of such printing systems, certain distinct subsystems of the machine are bundled together into modules which can be readily removed from the machine and replaced with new modules of the same type. A modular design facilitates a greater flexibility in the operation and maintenance of the machine.
As xerographic marking devices are now used for a variety of different applications, the requirement for printing on media of varying substrate weight and surface roughness has increased. Coated stock is widely used in the graphics art industry, which increasingly relies on xerographic marking devices.
However, current xerographic marking devices are generally optimized for a particular type of paper and thus may be unable to fuse other substrates without a significant slowing in productivity. Fusing tends to impart curl to the paper, which can cause paper jams downstream of the fuser. Additionally, paper jams and printer damage can occur when the paper finish is not fully compatible with the fusing process.
Integrated parallel printing systems have multiple fusers so the generally low reliability of color fusers has a significant impact on overall reliability. Additionally, maintaining gloss uniformity between the outputs of two or more marking devices is desirable. Deviations in gloss from one marking device to another exist due to tolerances in manufacturing, fuser conditions and components.